Hi Bill, 

v12.1 s over 10 years old. So there's no way that version could possibly be compatible with Net 5, which was only released recently. 

The latest version of the control are available for .Net 5, though. I'm not sure exactly what version we started supported .Net 5 in. I think it was 20.2 or maybe 21.1. 

Hi Geoff, 

So I have good news and bad news. 
I tried this out with v 21.1.32-ci and I am seeing the same exception you are getting: the NullReferenceException.
Then I tried this same thing with our latest internal build and I do not get that exception any more. So it looks like this will be fixed in the next service release. 
That's the good news. 

The bad news is that it looks like Visual Studio doesn't show a designer for Control-derived classes in Net Core. In DotNet Framework, they do. But in Net Core, they only show a designer surface for classes that derive from Form or UserControl. You can see this by creating a class that derives from Control. When I do this, I get an error message that there are no classes to be designed. 

Okay.. ignore the comments above. I finally realized that you are not right-clicking on the control on the form, but rather on the File in the Solution Explorer.

I tried this out with the latest ci build (32-ci) that you are using and I can reproduce the issue.

But when I try this with the latest internal version of the controls, I do not get the Exception. So it looks like this will be fixed in the next ci build or service release. 

However, even once that NullReferenceException is fixed, you still can't design the control, because Visual Studio gives me a different exception: 

"The designer could not be shown for this file because none of the classes within it can be designed."

But it looks like this is an issue with Visual Studio and not our controls, because I can reproduce the same issue with a control that is derived from Control, instead of UltraPanel. So there's nothing we can do about that.

So it appears that the VS Designer will only allow you to design certain classes like UserControl or Form and not classes that are derived from Control or other base classes like they do in DotNet Framework applications. 

I'm confused. 
Neither UltraPanel, nor the UserControl, nor the derived UltraPanel control have an option for "View Designer" on the context menu. 
I tried the "About" and "Custom Property Page" options, which are the only ones specific to UltraPanel that we provide and they are both working fine for me, at least with our latest internal build. 

Am I missing something? 

EDIT: 
Just to be extra thorough here, I tried it again with v21.1.32-ci and I still do not see a "View Designer" option on the context menu. 

Hi Joe, 

I'm confused. The issue reported here was already fixed a while ago, as I explained in my last reply. But this is regarding Windows Forms – it's nothing to do with Blazor. 

Hi Geoff, 

Pretty sure this is fixed in our latest bi-weekly build. Which means you can get it by checking the "Include prerelease" checkbox in the NuGet package manager in Visual Studio. 

Sorry, I was mistaken. It looks like the Service release is only for the older versions and doesn't include v21.1. 
So I'm not sure exactly when the fix for this issue will be released. Hopefully very soon.